Stack (geology) in the context of "Scott Island"

A natural arch, natural bridge, or (less commonly) rock arch is a natural landform where an arch has formed with an opening underneath. Natural arches commonly form where inland cliffs, coastal cliffs, fins or stacks are subject to erosion from the sea, rivers or weathering (subaerial processes).

Most natural arches are formed from narrow fins and sea stacks composed of sandstone or limestone with steep, often vertical, cliff faces. The formations become narrower due to erosion over geologic time scales. The softer rock stratum erodes away creating rock shelters, or alcoves, on opposite sides of the formation beneath the relatively harder stratum, or caprock, above it. The alcoves erode further into the formation eventually meeting underneath the harder caprock layer, thus creating an arch. The erosional processes exploit weaknesses in the softer rock layers making cracks larger and removing material more quickly than the caprock; however, the caprock itself continues to erode after an arch has formed, which will ultimately lead to collapse.

A skerry (/ˈskɛri/ SKERR-ee) is a small rocky island, or islet, usually too small for human habitation. It may simply be a rocky reef. A skerry can also be called a low sea stack.

Skerries may have vegetative life such as moss and small, hardy grasses. They are often used as resting places by animals such as seals and birds.

In Italian, faraglioni (pronounced [faraʎˈʎoːni]; Neapolitan: faragliune [faraʝˈʝuːnə]; singular faraglione in both languages) are stacks, coastal and oceanic rock formations eroded by waves.

The word may be derived from the Greek pháros or Latin pharus ("lighthouse") and is cognate with the Spanish farallón.

The Antipodes Islands (Māori: Moutere Mahue, lit. 'Abandoned Island') are inhospitable and uninhabited volcanic islands in subantarctic waters to the south of – and territorially part of – New Zealand. The 21 km (8.1 sq mi) archipelago lies 860 km (530 mi) to the southeast of Stewart Island / Rakiura, and 730 km (450 mi) to the northeast of Campbell Island.

The island group consists of one main island, Antipodes Island, of 20 km (7.7 sq mi) area, Bollons Island to the north, and numerous small islets and stacks.

The Needles are a row of three stacks of chalk that rise about 30 metres (98 ft) out of the sea off the western extremity of the Isle of Wight in the English Channel, United Kingdom, close to Alum Bay and Scratchell's Bay, and part of Totland, the westernmost civil parish of the Isle of Wight. The Needles Lighthouse stands at the outer, western end of the formation. Built in 1859, it has been automated since 1994. The waters and adjoining seabed form part of the Needles Marine Conservation Zone and the Needles along with the shore and heath above are part of the Headon Warren and West High Down Site of Special Scientific Interest.

The formation takes its name from a fourth needle-shaped pillar called Lot's wife, which collapsed in a storm in 1764. The remaining rocks are not at all needle-like, but the name has stuck.

Ball's Pyramid is an uninhabited islet in the Pacific Ocean located 20 kilometres (12 mi; 11 nmi) southeast of Lord Howe Island, between Australia and New Zealand. The steep rocky basalt outcrop is the eroded plug of a shield volcano and caldera that formed 6.4 million years ago. It is 572 metres (1,877 ft) high, 1,100 metres (3,609 ft) long and only 300 metres (984 ft) across, making it the tallest volcanic stack in the world.

Ball's Pyramid, which is part of Australia's Lord Howe Island Marine Park, is positioned in the centre of a submarine shelf surrounded by rough seas, which makes any approach difficult. The pyramid is home to the only remaining wild population of the giant Lord Howe Island stick insect, thought to be extinct since 1920 until their discovery in 2001.

Dryococelus australis, also known as the Lord Howe Island stick insect, Lord Howe Island phasmid or, locally, as the tree lobster, is a species of stick insect that lives in the Lord Howe Island Group. It is the only member of the monotypic genus Dryococelus. Thought to be extinct by 1920, it was rediscovered in 2001. Although it had been extirpated from Lord Howe itself, a remnant population of 24 individuals was rediscovered on the sea stack of Ball's Pyramid. The species has been called "the rarest insect in the world".